fix wu ke's unique k-best extraction bug
fix wu ke's unique k-best extraction bug

pks/cdec-dtrain-legacy,kho/mr-cdec,kho/mr-cdec,pks/cdec-dtrain-legacy,kho/mr-cdec,kho/mr-cdec,pks/cdec-dtrain-legacy,kho/mr-cdec,kho/mr-cdec,pks/cdec-dtrain-legacy,pks/cdec-dtrain-legacy,pks/cdec-dtrain-legacy